Say I have 10-20 different flipbook sequences in my mplay and I want to save them for later. I know you can save out individual flipbook sequences, but is it possible to save out every sequence at once? Or maybe save the mplay session which can be loaded back in?

The mplayer doesn't know anything about the contents of the frames. There's no such thing as a session-save. You'll need to write out the sequences one at a time, modifying the frame settings, or do it all at once then rename the frames yourself.

That's what I figured given the limited options in the interface.

Edit: I submitted an RFE to maybe get these mplay enhancements and add notes to the sequence list.